Multi-stage countercurrent hydrotreating process

ABSTRACT

A multi-stage process for removing heteroatoms, particularly organic sulfur and nitrogen components, from liquid petroleum and chemical streams. The feedstream flows countercurrent to the flow of a hydrogen-containing treat gas and is reacted with a first catalyst which is relatively tolerant to sulfur and nitrogen, such as a CoMo supported catalyst. When the level of organic sulfur in the feedstream is less than about 3,000 wppm and the level of organic nitrogen is less than about 1,000 wppm, the feedstream is reacted with said counter flowing hydrogen-containing treat gas in the presence of a catalyst comprised of Ni and a Group VIA metal selected from Mo, W, or both, on a refractory support. The reaction vessel preferably contains vapor and optionally liquid by-pass means in one or more of the catalyst beds.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part of U.S. Ser. No. 08/702,334 filedAug. 23, 1996.

FIELD OF THE INVENTION

[0002] The present invention relates to a countercurrent process forremoving heteroatoms, particularly organic sulfur and nitrogencomponents, from liquid petroleum and chemical streams. The feedstreamflows countercurrent to the flow of a hydrogen-containing treat gas andis reacted with a first catalyst which is relatively tolerant to sulfurand nitrogen, such as a CoMo supported catalyst. When the level oforganic sulfur in the feedstream is less than about 3,000 wppm and thelevel of organic nitrogen is less than about 1,000 wppm, the feedstreamis reacted with said counter flowing hydrogen-containing treat gas inthe presence of a catalyst comprised of Ni and a Group VIA metalselected from Mo, W, or both, on a refractory support. The reactionvessel preferably contains vapor and optionally liquid by-pass means inone or more of the catalyst beds.

BACKGROUND OF THE INVENTION

[0003] There is a continuing need in the petroleum refining and chemicalindustries for improved catalyst and process technology. One type ofprocess technology, which is often referred to as hydrotreating,involves the use of certain catalysts, typically those containing bothGroup VIA and Group VIII metals, for the removal of heteroatoms, such assulfur, nitrogen, and sometimes oxygen. More active catalysts andimproved reaction vessel designs are needed to meet this demand.Countercurrent reaction vessels have the potential of meeting some ofthis demand, but they have not done so to date because of the potentialfor upset. That is, upflowing treat gas has the potential of causingflooding of the reactor by preventing the feedstream from flowingthrough one or more catalyst beds. A two stage countercurrent process isdisclosed in U.S. Pat. No. 3,147,210 for thehydroprocessing-hydrogenation of high boiling aromatic hydrocarbons. Thefeedstock is first subjected to catalytic hydroprocessing, preferably inco-current flow with hydrogen, then subjected to hydrogenation over asulfur-sensitive noble metal hydrogenation catalyst countercurrent tothe flow of a hydrogen. U.S. Pat. Nos. 3,767,562 and 3,775,291 disclosea similar process for producing jet fuels, except the jet fuel is firsthydrodesulfurized prior to two-stage hydrogenation. U.S. Pat. No.5,183,556 also discloses a two-stage co-current/countercurrent processfor hydrofining - hydrogenating aromatics in a diesel fuel stream.

[0004] While the concept of countercurrent hydroprocessing has beenknown for some time, countercurrent flow reaction vessels are typicallynot used in the petroleum industry, primarily because, as previouslymentioned, conventional countercurrent reaction vessels are susceptibleto upset by catalyst bed flooding. While flooding is undesirable,catalyst contacting by the reactant liquid improves as the bedapproaches flooding conditions. However, operating close to the point ofincipient flooding leaves the process vulnerable to fluctuations inpressure or temperature or in liquid or gas flow rates. This couldresult in a disturbance large enough to initiate flooding and processunit shutdown, in order to recover stable operation. Such disruptionsare highly undesirable in a continuous commercial operation.

[0005] Reaction vessels have been disclosed in co-pending U.S. PatentApplications 08/775,636 and 08/775,638 both filed on Dec. 31, 1996, andboth entitled “Countercurrent Reactor”, and both of which areincorporated herein by reference. These applications disclosecountercurrent reactors which are less susceptible to flooding thanconventional countercurrent reaction vessels. This is primarily due tothe novel use of vapor passageways, or vapor by-pass means, which act toselectively bypass a fraction of the upward-flowing treat gas so it doesnot flow through one or more of the catalyst beds.

[0006] While the use of vapor by-pass means, typically tubes, has madethe use of countercurrent reactors more commercially feasible, there isstill a need in the art for improved catalyst staging in such vessels.

SUMMARY OF THE INVENTION

[0007] In accordance with the present invention, there is provided amulti-stage process for removing sulfur and nitrogen containingcomponents from petroleum and chemical feedstreams containing at leastone of said components, in the presence of a hydrogen-containing treatgas flowing countercurrent to the flow of said feedstream, the processwhich comprises:

[0008] reacting said feedstock in a first reaction stage with saidhydrogen-containing treat gas in the presence of a catalyst comprised ofCo and Mo on a refractory support until the reacted feedstock containsless than about 3,000 wppm sulfur and less than about 1,000 wppmnitrogen;

[0009] reacting said treated feedstock in a second stage withcounterflowing hydrogen-containing treat gas in the presence of acatalyst comprised of Ni and a Group VIA metal selected from one or bothof Mo and W, on a refractory support.

[0010] In one embodiment of the present invention the reaction vesselcontains a third reaction stage downstream of said second reactionstage, which third reaction stage contains a noble metal supportedcatalyst.

[0011] In another preferred embodiment of the present invention thethird reaction stage is an aromatics hydrogenation stage.

[0012] In still another embodiment of the present invention thefeedstock is reacted in the presence of the Ni/Group VIA metal catalystonly when its sulfur level reaches less than about 1,500 wppm and itsnitrogen level reaches less than about 750 wppm.

[0013] In yet another embodiment of the present invention at least someof the vapor passageways are external to the reaction vessel.

BRIEF DESCRIPTION OF THE FIGURES

[0014]FIG. 1 hereof is a reaction vessel of the present inventionshowing three reaction zones, each of which contains vapor passagewaysso that upflowing vapor can bypass a reaction zone, and one liquid drainmeans.

[0015]FIG. 2 is a representation of how the reaction vessel of FIG. 1will respond to a flooding situation while actions are taken to returnbed hydrodynamics to normalcy.

DETAILED DESCRIPTION OF THE INVENTION

[0016] In conventional countercurrent processing, the verticallyupflowing treat gas has the potential of hindering the downwardlyflowing liquid feedstream to such a degree to cause reactor flooding.That is, by not allowing liquid to drain through the catalyst bed(s) inthe reactor. At low liquid and gas velocities the hindrance from theslowly moving gas is not enough to cause flooding and the liquid in thereaction vessel is able to pass through the catalyst bed or beds.However, if either the upflowing gas rate or the downflowing liquid rateis high enough, liquid cannot drain through the catalyst bed. As theliquid holdup in a catalyst bed increases, liquid accumulates above thetop surface of the bed. The upflowing gas rate at which flooding occursin a given catalyst bed will depend on such things as the flow rate andthe physical properties of the downflowing liquid. Similarly, thedownflowing liquid flow rate at which flooding occurs in a given bedsimilarly depends on the rate and properties of upflowing gas.

[0017] The reaction vessels used in the practice of the presentinvention are less susceptible to flooding than conventionalcountercurrent reaction vessels because of vapor passageways which actto selectively bypass a fraction of the upward-moving treat gas so thatit does not flow through one or more of the catalyst beds. The fractionof upflowing treat gas that bypasses a catalyst bed will increase asvapor pressure drop increases through a catalyst bed. Thus, the vaporpassageways provide a self-adjusting regulation of upward-flowing vapor,thereby extending the hydrodynamic operating window of the reactionvessel. Further extension of this range can be provided by including oneor more external vapor passageways having flow control means. Such asystem provides a means by which catalyst bed pressure drop, andtherefore catalyst contacting efficiency, can be controlled. Preferably,when both internal and external vapor passageways are provided, theexternal vapor passageways can be controlled with a control means,preferably a valve for so-called “trim” bypassing. The valve of coursecan be automatically operated so that it opens and closes to theappropriate degree in response to a signal transmitted relating topressure drop changes in the catalyst bed(s). That is, the trim bypasswill be used to keep the reaction vessel operating as close to floodingas desirable. The remaining treat gas stream, which does not bypass aparticular catalyst bed or beds, will pass upward through the catalystbed(s) and take part in the desired hydrotreating reaction, carry awaylight or vaporized reaction products, and strip catalyst poisons such ashydrogen sulfide, water and/or ammonia, etc.

[0018] The vapor passageways of the reaction vessels used in thepractice of the present invention provide an extended operating rangeand an opportunity to operate close to the flooding point of thereaction vessel. This enables a more stable, more efficient reactionvessel operating regime. Further, the reaction vessel can safely andcontinuously operate while responding to normal process fluctuations intemperature and in liquid and vapor flow rate. The range of total flowrates that can be tolerated is thereby extended. Operating close to theflooding point results in very efficient contacting because the catalystparticles are well irrigated by the downflowing liquid. In the absenceof vapor passageways, a conventional countercurrent reaction vesselwould need to operate at lower efficiency in order to remain operable.The higher vapor flow rate capacity of the reaction vessels used in thepractice of the present invention provides flexibility to use higherquench gas rates and/or treat gas rates, enabling a wider breadth ofapplication for reactions involving high hydrogen consumption and heatrelease, such as aromatics saturation. Furthermore, the higher gashandling capacity enables the use of countercurrent reaction processingfor reactions involving evolution of vapor phase products which mightotherwise result in flooding due to excessive vapor generated duringreaction, e.g., hydrocracking.

[0019] When flooding does occur, the reaction vessels used in thepractice of the present invention are also more easily recovered andbrought back to normal operation. During flooding, the liquid holdup ina catalyst bed increases and liquid may begin to accumulate above thetop surface of the catalyst bed. This liquid must be drained to recoverthe reactor from a flooded state. The vapor passageways reduce gas flowrate through the catalyst bed(s), thus allowing the liquid to moreeasily drain through the catalyst bed(s). The liquid drain means of thepresent invention also helps recover the reaction vessel from flooding.Unless otherwise stated herein, the terms “downstream” and “upstream”are with respect to the flow of liquid which will flow downward.

[0020] The reaction vessels used in the practice of the presentinvention can be better understood by a description of an examplereaction vessel, which is shown in FIGS. 1 and 2 hereof. Miscellaneousreaction vessel internals, such as flow distributor means,thermocouples, heat transfer devices etc. are not shown in the figuresfor simplicity. FIG. 1 shows reaction vessel R which contains liquidinlet LI for receiving a feedstock to be treated, and a liquid outlet LOfor removing liquid reaction product. There is also provided treat gasinlet GI and gas outlet GO. The reaction vessel contains threevertically disposed reaction zones, r₁, r₂, and r₃. Each reaction zoneis immediately preceded and immediately followed by a non-reaction zone,nr₁, nr₂, nr₃, and nr₄. The non-reaction zone may be a void, or emptysection, in the reaction vessel. That is, a section which does notcontain catalyst. Liquid distribution means LR (which is not shown inFIG. 2 for simplicity) can be situated above each reaction zone in orderto more evenly distribute downflowing liquid to the next downstreamreaction zone. Each reaction zone is comprised of a bed of catalystsuitable for the desired reaction.

[0021] Hydrotreating catalysts which are relatively tolerant to sulfurand nitrogen will be used in the first catalyst stage. By “tolerant tosulfur and nitrogen” we mean catalysts that are not as easily poisonedby sulfur and nitrogen as is a NiMo catalyst. Such sulfur/nitrogentolerant catalysts will typically be those containing at least one GroupVIII metal, preferably Fe or Co, more preferably Co; and at least oneGroup VIA metal, preferably Mo and W, more preferably Mo, on a highsurface area support material, preferably alumina. The Groups referredto herein are from the Period Table of the Elements, Sargent-WelchScientific Co., 1980, Catalog No. S-18806. The Group VIII metal istypically present in the an amount ranging from about 2 to 20 wt. %,preferably from about 4 to 12%. The Group VIA metal will typically bepresent in an amount ranging from about 5 to 50 wt. %, preferably fromabout 10 to 40 wt. %, and more preferably from about 20 to 30 wt. %. Allmetals weight percents are on support. By “on support” we mean that thepercents are based on the weight of the support. For example, if thesupport were to weigh 100 g. then 20 wt. % Group VIII metal would meanthat 20 g. of Group VIII metal was on the support. It is within thescope of the present invention that more than one type ofsulfur/nitrogen hydrotreating catalyst be used in this first reactionstage. For example, two or more different hydrotreating catalysts can beblended together and used in a mixed catalyst bed. Further, two or morehydrotreating catalysts can be extruded together so that they arecomposited in the same extrudate. Also, two or more hydrotreatingcatalysts can be used in separate catalyst beds, preferably fixed beds,wherein each catalyst bed will represent a catalyst zone within the samesingle catalyst stage. That is, each catalyst stage can contain morethan one catalyst zones. Typical hydrotreating temperatures will rangefrom about 100° C. to about 400° C. at pressures from about 50 psig toabout 2,000 psig. Liquid hourly space velocities are from about 0.2 to10 volumes of liquid per volume of catalyst per hour. Typical treat gasrates are from about 200 to about 3,000 SCF hydrogen-rich gas per barrelof feedstock.

[0022] It has been found by the inventors hereof that when thefeedstream contains less than about 3,000 wppm, preferably less thanabout 1,500 wppm, and more preferably less than about 1,000 wppm sulfur;and less than about 1,000 wppm, preferably less than about 750 wppm, andmore preferably less than about 500 wppm nitrogen, a catalyst comprisedof Ni and one or both of Mo and W will remove unexpectedly more of theremaining sulfur and nitrogen components when compared to otherconventional hydrotreating catalyst. Such catalysts include NiMo, NiW,and Ni-Mo-W, on a refractory support. Preferred are NiMo and Ni-Mo-W.Thus, it is critical to the present invention that the portion of thereaction zone, where the feedstream contains said low levels of sulfurand nitrogen components be subjected to a said Ni-based supportedhydrotreating catalyst.

[0023] It is within the scope of the present invention that additionalreaction stages can follow the second reaction stage containing theNi/Group VIA metal catalyst. One such stage can be an aromaticshydrogenation stage containing a noble metal sulfur sensitivehydrogenation catalyst. Non-limiting examples of noble metal catalystsinclude those based on platinum and/or palladium, which is preferablysupported on a suitable support material, typically a refractory oxidematerial such as alumina, silica, alumina-silica, kieselguhr,diatomaceous earth, magnesia, and zirconia. Zeolitic supports can alsobe used. Such catalysts are typically susceptible to sulfur and nitrogenpoisoning. The aromatic saturation zone is preferably operated at atemperature from about 40° C. to about 400° C., more preferably fromabout 260° C. to about 350° C., at a pressure from about 100 psig toabout 3,000 psig, preferably from about 200 psig to about 1,200 psig,and at a liquid hourly space velocity (LHSV) of from about 0.3 V/V/Hr.to about 2.0 V/V/Hr.

[0024] A hydrocracking reaction stage can also be present downstream ofthe NiMo reaction stage. If one of the downstream reaction zones is ahydrocracking zone, the catalyst can be any suitable conventionalhydrocracking catalyst run at typical hydrocracking conditions. Typicalhydrocracking catalysts are described in U.S. Pat. No. 4,921,595 to UOP,which is incorporated herein by reference. Such catalysts are typicallycomprised of a Group VIII metal hydrogenating component on a zeolitecracking base. The zeolite cracking bases are sometimes referred to inthe art as molecular sieves, and are generally composed of silica,alumina, and one or more exchangeable cations such as sodium, magnesium,calcium, rare earth metals, etc. They are further characterized bycrystal pores of relatively uniform diameter between about 4 and 12Angstroms. It is preferred to use zeolites having a relatively highsilica/alumina mole ratio greater than about 3, preferably greater thanabout 6. Suitable zeolites found in nature include mordenite,clinoptiliolite, ferrierite, dachiardite, chabazite, erionite, andfaujasite. Suitable synthetic zeolites include the Beta, X, Y, and Lcrystal types, e.g., synthetic faujasite, mordenite, ZSM-5, MCM-22 andthe larger pore varieties of the ZSM and MCM series. A particularlypreferred zeolite is any member of the faujasite family, see Tracy etal. Proc. of the Royal Soc., 1996, Vol. 452, p813. It is to beunderstood that these zeolites may include demetallated zeolites whichare understood to include significant pore volume in the mesopore range,i.e., 20 to 500 Angstroms. Non-limiting examples of Group VIII metalswhich may be used on the hydrocracking catalysts include iron, cobalt,nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum.Preferred are platinum and palladium, with platinum being morepreferred. The amount of Group VIII metal will range from about 0.05 wt.% to 30 wt. %, based on the total weight of the catalyst. If the metalis a Group VIII noble metal, it is preferred to use about 0.05 to about2 wt. %. Hydrocracking conditions include temperatures from about 200°to 425° C., preferably from about 220° to 330° C., more preferably fromabout 245° to 315° C.; pressure of about 200 psig to about 3,000 psig;and liquid hourly space velocity from about 0.5 to 10 V/V/Hr, preferablyfrom about 1 to 5 V/V/Hr.

[0025] Five vapor passageways VB₁, VB₂, VB₃, VB₄, and VB₅ and one liquiddrain means LD are shown for the reaction vessels of the Figures,although any number and size of the vapor passageways can be useddepending on the portion of the vapor one wishes to bypass the reactionzone(s). For purposes of the present invention, it is desirable thatonly a portion of the vapor bypasses one or more countercurrent reactionzones. It is preferred that less than about 50 vol. %, more preferablyless than about 25 vol. %, and most preferably less than about 10 vol. %of the vapor bypasses any individual countercurrent reaction zone. Theliquid drain means serves as a vapor passageway during normal operationbut can allow liquid to drain during flooding upsets. It is to beunderstood that more than one liquid drain means can be used in any oneor more reaction zones. The size and number of such liquid drain meanswill be dependent on such things as the size of the reaction vessel, thepacking of the catalyst in the catalyst bed(s) and the flow rate ofliquid feedstock through the catalyst bed.

[0026] The reaction vessel of FIG. 1 is operated by introducing thefeedstock to be treated into liquid inlet LI of reaction vessel R. Asuitable treat gas, such as a hydrogen-containing gas, is introduced viaport GI into the reaction vessel countercurrent to the downward flow ofthe liquid feedstock. The term “hydrogen-containing treat gas” means atreat gas stream containing at least an effective amount of hydrogen forthe intended reaction. The treat gas stream will preferably contain atleast about 50 vol. %, more preferably at least about 75 vol. %hydrogen. It is also preferred that the hydrogen-containing treat gas bemake-up hydrogen-rich gas, preferably hydrogen. It is to be understoodthat the treat gas need not be introduced solely at the bottom of thereaction vessel at GI, but may also be introduced into any one or moreof the non-reaction zones, for example at GI_(a) and/or GI_(b). Treatgas can also be injected into any one or more of the catalyst beds. Anadvantage of introducing treat gas at various points in the reactionvessel is to control the temperature within the reaction vessel. Forexample, cold treat gas can be injected into the reaction vessel atvarious points to moderate any exothermic heat of reaction. It is alsowithin the scope of this invention that all of the treat gas can beintroduced at any one of the aforesaid points as long as at least aportion of it flows countercurrent to the flow of liquid in at least onereaction zone.

[0027] The reaction vessels of the present invention are operated atsuitable temperatures and pressures for hydrotreating reactions. Theliquid feedstock passes downward through the catalyst bed of reactionzone r₁, where it reacts with the treat gas on the catalyst surface. Anyresulting vapor-phase reaction products are swept upwards by theupward-flowing treat gas. Such vapor-phase reaction products may includerelatively low boiling hydrocarbons and heteroatom components, such asH₂S and NH₃. Any unreacted feedstock, as well as liquid reaction productpasses downwardly through each successive catalyst bed of eachsuccessive reaction zone r₂ and r₃. This Figure shows an optional liquiddistribution means LR which can be positioned above each catalyst bed.The ends of the vapor passageways may be situated above or below theliquid distribution means. For example, FIG. 1 shows the upper end ofvapor passageway VB₃ terminating at a point above liquid distributionmeans LR. The lower end of vapor passageways VB₁ and VB₂ terminate at apoint below the liquid redistribution means LR. This arrangement allowsselective bypassing of vapors produced in reaction zone r₂ to thereaction vessel gas outlet, while bringing a higher purityhydrogen-containing treat gas into catalyst bed r₁ by selectivelybypassing higher-purity hydrogen-containing gas from nr₃ to the inlet ofcatalyst bed r₁. It is within the scope of this invention that the upperor lower ends of one or more of the vapor passageways terminate at apoint within the reaction zone. The reaction vessel may employ anyconventional distribution trays, such as sieve trays, bubble cap trays,etc. The liquid effluent exits the reaction vessel via port LO and vaporeffluent via port GO. The preferred mode of operation of the reactionvessels of the present invention is to bypass only a portion of thevapor while still maintaining enough vapor upflowing through thecatalyst bed(s) to meet the treat gas (hydrogen) demand for thatcatalyst bed(s) with relatively high kinetic efficiency.

[0028] As previously mentioned, countercurrent reaction vessels aretypically susceptible to upset by flooding. That is, the upflowing treatgas can prevent liquid feedstock and liquid effluent from flowingdownward through one or more catalyst beds. FIG. 2 hereof depicts howthe reaction vessel of FIG. 1 would operate during a flooding situationto get the reaction vessel back on-stream without substantial downtime.For example, during a flooding situation in reaction zone r₂, liquidholdup in the bed increases and liquid may begin to accumulate above thetop surface of the catalyst bed. One or more liquid drain means LD areprovided to allow the liquid to bypass one or more catalyst beds. Priorto flooding, the liquid drain means will act as a vapor passageway. Thetop of the liquid drain means can be flush with, or any height above thetop surface of the catalyst bed. It is preferred that the top of theliquid drain means be substantially flush with the top surface of thecatalyst bed. Any liquid that passes through the drain means can bepassed to the next downstream bed or it can preferably be recycled toany one or more reaction zones.

[0029] The vapor and liquid drain passageways may be any suitablestructure constructed from a material that can withstand the operatingconditions of the reaction vessel. Suitable materials include metals,such as stainless and carbon steels; ceramic materials; as well as highperformance composite materials such as carbon fiber materials.Preferred are tubular passageways. The passageways need not be perfectlyvertical. That is, they can be inclined or curved, or even in the formof a spiral. They can also be perforated along the sides. It is to beunderstood that the passageways can be of any suitable size depending onthe amount and rate of vapor one wishes to pass from one non-reactionzone to another. Further, one or more of the passageways, or drainmeans, can have a flat substantially horizontal member, such as abaffle, above it to prevent liquid from an upstream bed from fallinginto the passageways. Also, more than one passageway can be extendedthrough at least a portion of any one or more reaction zones. It ispreferred that the vapor passageways be extended entirely through theone or more reaction zones. When a plurality is used it is preferredthat they be concentrically located about the vertical axis of thereaction vessel. One or more vapor passageways can also be routedexternal to the reaction zone. For example, a tubular arrangement can beused on the outside of the reaction vessel so that one or morenon-reaction zones are in fluid communication with any one or more othernon-reaction zones. The vapor passageways may contain a flow controlmeans to control the portion of vapors which is passed from onenon-reaction zone to another non-reaction zone. If the vapor passagewaysare external to the reaction vessel, then it is preferred that the flowcontrol means be simply a flow control valve.

[0030] It is within the scope of the present invention that the vaporpassageways bypass two or more catalyst beds, or reaction zones.Further, the vapor passageways need not be hollow structures, such assolid-walled tubes, but they may contain a packing material, such asinert balls. The packing material in the vapor passageways can be of adifferent size than the catalyst particles in the catalyst beds of thereaction zones. Such packing may help to improve the bypassingcharacteristics of said tubes. TIt is preferred that one or moreco-current reaction zones be upstream of one or more countercurrentreaction zones. The zones can be in separate vessels or two or morezones can be in the same vessel. It is preferred that all countercurrentzones be in the same vessel.

[0031] Feedstocks suitable for use in the practice of the presentinvention include those in the naphtha boiling range to heavyfeedstocks, such as gas oils and resids. Typically, the boiling rangewill be from about 50° C. to about 1000° C.. Non-limiting examples ofsuch feeds which can be used in the practice of the present inventioninclude vacuum resid, atmospheric resid, vacuum gas oil (VGO),atmospheric gas oil (AGO), heavy atmospheric gas oil (HAGO), steamcracked gas oil (SCGO), deasphalted oil (DAO), and virgin and crackeddistillates and mixtures thereof.

[0032] In the case where the first reaction zone is a co-currenthydrotreating reaction zone, the liquid effluent from said hydrotreatingreaction zone will be passed to at least one downstream reaction zonewhere the liquid is passed through a bed of catalyst countercurrent tothe flow of upflowing hydrogen-containing treatgas. Depending on thenature of the feedstock and the desired level of upgrading, more thanone reaction zone may be needed. For example, the first stage containingthe sulfur/nitrogen tolerant catalyst can consist of two catalyst zones.The first catalyst zone of the first stage can be a co-current catalystzone and the second a countercurrent catalyst zone.

[0033] The liquid phase in the reaction vessels of the present inventionwill typically be comprised of the higher boiling point components ofthe feed. The vapor phase will typically be a mixture ofhydrogen-containing treat gas, heteroatom impurities, and vaporizedlower-boiling components of the fresh feed, as well as light products ofhydroprocessing reactions. The vapor phase in the catalyst bed of acountercurrent reaction zone will be swept upward with the upflowinghydrogen-containing treat gas and collected, fractionated, or passedalong for further processing. If the vapor phase effluent still containsan undesirable level of heteroatoms and/or aromatics, it can be passedto a vapor phase reaction zone containing additional hydrotreatingcatalyst and subjected to suitable hydrotreating conditions for furtherremoval of heteroatoms. It is to be understood that all reaction zonescan either be in the same vessel separated by non-reaction zones, or anycan be in separate vessels. The non-reaction zones in the later case,will include the transfer lines leading from one vessel to another.

[0034] In an embodiment of the present invention, the feedstock can beintroduced into a first catalyst zone co-current with the flow ofhydrogen-containing treat-gas and reacted with a sulfur/nitrogentolerant catalyst. A vapor phase effluent fraction can then be separatedfrom the liquid phase effluent fraction between reaction zones. That is,in a non-reaction zone. The vapor phase effluent can be passed toadditional hydrotreating, or collected, or further fractionated. Theliquid phase effluent will then be passed to the next downstreamreaction zone, which will preferably be a countercurrent reaction zone.If the sulfur and nitrogen levels are below the 3,000/1,000 wppm levelsrespectively, this countercurrent zone can in fact be the secondreaction stage containing the NiMo catalyst. If the levels of sulfur andnitrogen are still too high, then this countercurrent zone can containanother sulfur/nitrogen tolerant hydrotreating catalyst. In otherembodiments of the present invention, vapor phase effluent and/or treatgas can be withdrawn or injected between any reaction zones.

[0035] The countercurrent contacting of liquid from an upstream reactionzone with upflowing threat gas strips dissolved H₂S and NH₃ impuritiesfrom the effluent stream, and results in greater hydrogen partialpressure and improved catalyst performance downstream. The resultingfinal liquid product will contain a substantially lower level ofheteroatoms and somewhat more hydrogen content than the originalfeedstock. This liquid product stream may be sent to downstreamhydroprocessing or conversion processes.

What is claimed is:
 1. A multi-stage process for removing sulfur andnitrogen containing components from petroleum and chemical feedstreamscontaining at least one of said components, in the presence of ahydrogen-containing treat gas flowing countercurrent to the flow of saidfeedstream, the process which comprises: reacting said feedstock in afirst reaction stage with said hydrogen-containing treat gas in thepresence of a hydrotreating catalyst comprised of at least one GroupVIII metal and at least one Group VIA metal on a refractory support, athydrotreating conditions, until the reacted feedstock contains less thanabout 3,000 wppm sulfur and less than about 1,000 wppm nitrogen;reacting said treated feedstock from said first reaction stage in asecond stage with counterflowing hydrogen-containing treat gas in thepresence of a catalyst comprised of Ni and one or both of a metalselected from Mo and W, on a refractory support.
 2. The process of claim1 wherein the hydrotreating conditions include temperatures ranging fromabout 100° C. to about 400° C. at pressures from about 50 psig to about2,000 psig.
 3. The process of claim 1 wherein the Group VIII metal is Coand the Group VIA metal is Mo.
 4. The process of claim 1 wherein thefirst reaction zone is operated in a co-current mode wherein thefeedstream and the treat gas are both flowing in the same direction. 5.The process of claim 1 wherein both the first and the second reactionstages are operated in countercurrent mode wherein the feedstream andthe treat gas flow countercurrent to each other.
 6. The process of claim1 wherein the amount of Group VIII metal is from about 2 wt. % to 20 wt.%, based on the total weight of the catalyst.
 7. The process of claim 1wherein the amount of Group VIA metal is from about 5 to about 50 wt. %,based on the total weight of the catalyst.
 8. The process of claim 3wherein 2 wherein the Group VIII metal is Co and the Group VIA metal isMo.
 9. A multi-stage process for removing sulfur and nitrogen containingcomponents from petroleum and chemical feedstreams containing at leastone of said components, in the presence of a hydrogen-containing treatgas flowing countercurrent to the flow of said feedstream, the processwhich comprises: reacting said feedstock in a first reaction stage withsaid hydrogen-containing treat gas in the presence of a hydrotreatingcatalyst comprised of at least one Group VIII metal and at least oneGroup VIA metal on a refractory support, at hydrotreating conditions,until the reacted feedstock contains less than about 3,000 wppm sulfurand less than about 1,000 wppm nitrogen; reacting said treated feedstockfrom said first reaction stage in a second stage with counterflowinghydrogen-containing treat gas in the presence of a catalyst comprised ofNi and one or both of a metal selected from Mo and W, on a refractorysupport; and reacting the treated feedstock from said second reactionstage in a third reaction stage in the presence of a hydrogen-containingtreat gas and an aromatics hydrogenation catalyst comprised of a noblemetal on a refractory support at hydrogenation conditions.
 10. Theprocess of claim 9 wherein the hydrotreating conditions includetemperatures ranging from about 100° C. to about 400° C. at pressuresfrom about 50 psig to about 2,000 psig.
 11. The process of claim 10wherein the Group VIII metal is Co and is present in an amount rangingfrom about 2 wt. % to 20 wt. %, and the Group VIA metal is Mo in anamount ranging from about 5 to 50 wt. %, based on the total weight ofthe catalyst.
 12. The process of claim 11 wherein the first reactionzone is operated in a co-current mode wherein the feedstream and thetreat gas are both flowing in the same direction.
 13. The process ofclaim 11 wherein both the first reaction stage is operated in co-currentmode and the second and third reaction stages are operated incountercurrent mode wherein the feedstream and the treat gas flowcountercurrent to each other.
 14. The process of claim 11 wherein theall three stages are operated in countercurrent mode.